tends to split everything/everyone into those on the inside or outside of the gate.

I think this is related to the affinity group/web of trust that anarchists tend to use, and ties into his larger point: "Anarchist recruitment for decades had been primarily social / subcultural". It's always been gatekeepy and personal, and therefore people who just google "democratic socialism" because Bernie aren't going to find any welcoming anarchists because there's not going to be an "anarchist worker's party" recruiting members.